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This invention relates to an improvement in the Instrument Landing System (ILS) for aircraft, in particular, the glide slope component thereof, employing an antenna system of the earth-image type, such as described in Butts, H. H., U.S. Pat. No. 3,325,812, Jun. 13, 1967, Capture Effect Glide Slope System, (Ref.1).
The standard antenna usually is mounted on a steel tower located several hundred feet to one side of the runway, considered a safe distance to avoid being struck by an airplane. This invention, however, is an antenna using wide aperture slotted cable elements, such as described in U.S. Pat. No. 4,464,665, Aug. 7, 1984, Watts, Jr., (Ref.2), or in co-pending application xe2x80x9cImprovement in Slotted Cable Antenna Structure.xe2x80x9d Frangible construction permits it to be located safely much closer to the runway. These characteristics allow for a guidance radiation pattern having narrow azimuthal coverage, resulting in improved glide slope performance in the vertical plane, together with fly-up signal to both sides as well as below path.
The invention is an improvement on standard ILS image-type glide slope antenna arrays. It replaces the usual antenna elements with wide aperture slotted cables. Mounted on a frangible support, the antenna array can be located safely much closer to the runway. The closer spacing, with the wide aperture, provides for a vertical guidance pattern that is narrower in azimuth, resulting in improved quality of guidance. An additional slotted cable, fed only with clearance signal, provides fly-up indication, both sides, over a wider azimuth sector.